It comes after weeks of protesting at the worksite where many people have been arrested and issued with move-on notices.

Roe 8 will be WA's first toll road despite state government indecision on the rest of the route for the $1.9 billion Perth Freight Link project connecting Roe Highway to Fremantle port.

Ms Ward said there were better freight solutions that did not cause so much destruction.

"I have never considered doing anything like this before but this project is so offensive, so destructive that it calls on normal people like myself to make a stand," she said.

"Today I am standing for our natural environment and a sustainable future, I am standing for our indigenous people whose land is being desecrated by this reckless vandalism."

Last week, protest group Save Beeliar Wetlands lost its bid to challenge state environmental approval for the road in the High Court, and is now pursuing a legal challenge in the Federal Court over Commonwealth environmental approval.

WA Environment Minister Albert Jacob says land clearing may be complete by the March state election.

Opposition Leader Mark McGowan said he did not condone the actions of the two women, but he did support the protesters and urged them to direct their concerns to the premier.

Premier Colin Barnett said it seemed many were "professional protesters" rather than locals, adding that the full force of the law would be used to arrest anyone who interfered with the project.

"We will not allow individuals to put their own lives and others in danger," he said.

"We won't allow them to interfere with the construction of the project, which has been through every process - environmental, legal - and has been part of Perth's long-term planning for 50 years."